We propose to investigate the effect of white light on the messenger RNA for the small subunit of ribulose 1,5 disphosphate carboxylase in Lemna gibba G3. The messenger for this protein is detected by translation in an in vitro protein synthesizing system from wheat germ followed by immunoprecipitation with antiserum to the small subunit. No small subunit mRNA can be detected in tissue from plants put into darkness for 4 days. Returning the plants to white light results in an increase in the amount of this poly A mRNA. We will investigate the kinetics of this response and try to determine whether the step(s) regulated by the action of light involve transcriptional, post-transcriptional, or translational processes.